High spatial resolution, low-noise Brillouin dynamic gratings reflectometry based on digital pulse compression

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Measurement Techniques
• Advanced Signal Processing

Background:

• Optical time-domain reflectometry (OTDR) is crucial for fiber optic diagnostics.
• Brillouin dynamic gratings (BDGs) offer unique capabilities for OTDR but face signal-to-noise challenges.
• Enhancing BDG performance requires advanced coding and detection strategies.

Purpose of the Study:

• To improve the performance of optical time-domain reflectometry (OTDR) using Brillouin dynamic gratings (BDGs).
• To address fundamental issues in BDG field-reflection and establish guidelines for coding and detection.
• To demonstrate enhanced signal-to-noise ratio (SNR) and spatial resolution in Brillouin gain spectrum (BGS) measurements.

Main Methods:

• Implementation of digital pulse compression techniques with BDGs in polarization-maintaining fibers.
• Formulation of rules for selecting appropriate coding and detection methods for BDG applications.
• Development and application of a 256-bit Golay complementary unipolar probe code.
• Establishment of conditions for utilizing direct detection in BDG-based OTDR.

Main Results:

• Achieved an eightfold enhancement in signal-to-noise ratio (SNR) for Brillouin gain spectrum (BGS) measurements.
• Demonstrated a spatial resolution of 2 cm.
• Attained a full-BGS acquisition rate of 133⅓ kHz.
• Significantly reduced the estimation error for small Brillouin frequency shifts.

Conclusions:

• Digital pulse compression is highly effective for enhancing BDG-based OTDR performance.
• The developed coding and detection strategies enable high-resolution and high-speed BGS measurements.
• This advancement has significant implications for precise fiber optic sensing and diagnostics.